451
Inorg. Chem. 1980, 19, 451-455 of molecular hydrogen. The nonbridge hydrogens appear to be favored in the nonstatistical distribution of the product. This supports the arguments that the hydrogen molecule is formed in a concerted reaction with Hg(3P,). The coordination of the Hg(3Pl) atom to a pair of hydrogen atoms in pentaborane results in the formation of the hydrogen molecule. Structures I and I1 in reaction 22 are a schematic repre-
sentation of the interaction. A similar interpretation is reported
for the Hg(3Pl) photosensitization of propane.20 The side-on orientation of Hg to H2 is consistent with Callear’s2’ study of the reaction of Hg(3Pl,o)with hydrogen. Acknowledgment. We are grateful for support of this work by the National Science Foundation (Grant No. C H E 7602477). Registry No. B5H9, 19624-22-7; B5D9, 24034-84-2; 1-DB5Hs, 63643-91-4; (p-D)B,Hs, 16743-79-6; 1-methylpentaborane,1949555-7; 2-methylpentaborane, 23753-74-4. (20) J. G. Calvert and J. N. Pitts, Jr., “Photochemistry”, Wiley, New York, 1966, p 97. (21) A. B. Callear and J. McGurk, J . Chem. SOC.,Faraday Trans. 2,68,289 (1972).
Contribution from the Departments of Chemistry, University of New Hampshire, Durham, New Hampshire 03824, and Fordham University, Bronx, New York 10458
Boron Halide Clusters and Radicals: Synthesis and Interconversions of the Three Oxidation States of a Nine-Boron Polyhedron EDWARD H. WONG*’ and RAIFAH M. KABBANI Received June 12, 1979
The facile synthesis of the perhalogenated nonahydrononaborates B9X92-(X = CI, Br, I) under aprotic conditions from B9H92-is described. Oxidations of the perchloro and perbromo anions have yielded the corresponding neutral clusters B9C19 and B9Br9.Novel borane radicals of the type B9X9-. (X = C1, Br, I) have been isolated as air-stable,colored salts via chemical oxidation of B9X92-or reduction of B9X9.The redox sequence B9X9*-* B9X9-.+ B9X9has been established. It is likely that all three oxidation states retain the basic tricapped trigonal-prismatic(&) geometry characteristic of the parent B9H92structure. This behavior is unusual for nonmetallic polyhedra, and extensive involvement of the halogen substituents in cage bonding is suggested.
Introduction The family of polyhedral boranes B,H;- (6 I n I12) have exceptional stability as predicted by theoretical MO calculations and empirical electron-counting rule^.^,^ These species have closed-shell electron configurations with the requisite (2n 2 ) skeletal electrons. Formally, the (2n + 1) family of B,Hp radicals and 2n neutral B,H, species can be generated by one- and two-electron oxidations, respectively. Indeed an EPR spectrum from the probable BloHlo-.radical has been observed in the electrolytic oxidation of B10H102-.4 A wellresolved, complex EPR spectrum obtained during the air oxidation of B9H,2- in ethereal solvents has been used to support the existence of BsHs-. as one of the transient products.s Nevertheless, neither of these unstable anions was isolable.
Scheme I
,a> B9Clgz-
(30
60%)
+
University of New Hampshire. (a) W. N. Lipscomb, “Boron Hydrides”, Benjamin, New York, 1963; (b) E. L. Muetterties and W. H. Knoth, “Polyhedral Boranes”, Marcel Dekker, New York, 1968; (c) D. A. Dixon, D. A. Kleier, T. A. Halgren, J. H. Hall, and W. N. Lipscomb, J . Am. Chem. SOC.,99,6226 (1977); (d) Jun-ichi Aihara, ibid., 100, 3339 (1978); (e) M. J. S . Dewar and M. L. McKee, Inorg. Chem., 17, 1569 (1978). (a) R. E. Williams, Inorg. Chem., 10, 210 (1971); (b) K. Wade, J . Chem. SOC., Chem. Commun., 792 (1971); (c) K. Wade, Inorg. Nucl. Chem. Lett., 8,559, 563,823 (1972); (d) K. Wade, Adu. Inorg. Chem. Radiochem., 18, 1 (1976); (e) R. W. Rudolph, Arc. Chem. Res., 9,446 (1976). (a) A. Kaczmarczyk, R. D. Dobrott, and W. N. Lipscomb, Proc. Natl. Acad. Sci. U.S.A.48,729 (1962); (b) J. S. Lewis and A. Kaczmarczyk, J . Am. Chem. SOC.,88, 1068 (1966); (c) R. L. Middaugh and F. Farha, Jr., ibid., 88, 4147 (1966). F. Klanberg, D. R. Eaton, L. J. Guggenberger, and E. L. Muetterties, Inorg. Chem., 6, 1271 (1967).
0020-1669/80/1319-0451$01,00/0
k>-:IgB
(70
80%)
The hypothetical B,H, neutral boranes should be extremely unstable and none has been observed to date. In sharp contrast, the perhalogenated derivatives of these boranes are well established in both the dianionic and neutral oxidation states. For example, Bl0Cll,,-, BIOBr12-,B12C1122-, and Bl2BrlZ2-are known as are the neutral clusters B4C14, B8Cls, B,Cl,, B9Br9,and B9C18H.6,7Massey’s investigations have definitively established the existence and geometry of the neutral nine-boron halide clusters and B9Br9.7b17dThe stability of these clusters in spite of their being formally two-electron deficient (2n skeletal electrons) has been postu(6) W. H. Knoth, H. C. Miller, J. C. Sauer, J. H. Balthis, Y. T. Chia, and E. L. Muetterties, Inorg. Chem., 3, 159 (1964). (7) (a) G. Urry, T. Wartik, and H. I. Schlesinger, J . Am. Chem. SOC.,74, 5809 (1952); (b) G. F. Lanthier and A. G. Massey, J . Inorg. Nucl. Chem., 32, 1807 (1970); (c) G. F. Lanthier, J. Kane, and A. G. Massey, ibid., 33, 1569 (1971); (d) M. S . Reason and A. G. Massey, ibid., 37, 1593 (1974); (e) J. A. Forstner, F. E. Haas, and E. L. Muetterties, Inorg. Chem., 3, 155 (1964).
0 1980 American Chemical Society
Wong and Kabbani
452 Inorganic Chemistry, Vol. 19, No. 2, 1980
Table I. Electronic Absorption Bands for the B,Xv2- and B,X;. Boranes in Acetonitrile dianion B,Cl,*B,Brq2B,Ig2-
,,,,A nm 225 237 221 sh, 266 SII
anion B,Cl,-. B,,Brq-. B,I,-.
&ax, nm 275, 425 278 sh, 349, 480 228, 255 sh, 563
Table It. “ B N M R Data of B,Xy2-
~
_
_
anion B,Cl,*B,Br,’B,I,’-
_
chem shifts, ppma re1 intens __________ -~ 1 .45,b -~
5.49 -~0.77,-8.15 -3.14, -16.00
a Chemical shifts relative to BI:, .Et,O. nance at -5.49 ppm.
1200
I000
@GO
3:6 3:6 3:6 Shoulder to the reso-
E
WAVE NU’VIBER ( c d )
Figure 1. Comparison of the IR spectra of B9C1?-, BgBr?-, and B,I?-.
lated as owing to extensive halogen back-donation into the polyhedra.3e These two classes of boron clusters are formally related bq two-electron redoxes, yet no interconversions have been demonstrated for them. A serendipitous preparation of B9C18H2-was reported via the “hydrolysis” of B9C18H,but the mode of formation of the dianion from the neutral cluster was obscured.’e In order to establish the redox relationship between these neutral clusters and their dianions, we sought to prepare the perhalogenated B9H92-derivatives and to study their oxidations. Further impetus for this work was provided by the dearth of derivative chemistry for the smaller and less symmetrical polyhedral boranes. To date, only the Blo and B12 dianions have well-defined substitution chemistry.2b It was also deemed reasonable that intermediate monoanionic radicals of the type B9X9-. may be sufficiently stable for isolation. N o polyhedral borane radicals of this type have been reported. Our preliminary communication on the BgC1g2-synthesis and its interconversions with B9CI9has appeared.* We report here an improved synthesis and its extension to B9Brg2-,B91g2-,and B9Br9,as well as the isolation of the first stable radicals of the B,X,-. family. Results and Discussion B9Xg2-. Since the air and hydrolytic instability of B9H92precludes its perhalogenation under protic conditions, halogenations were performed with the tetra-n-butylammonium salt of B9H92-in methylene chloride under a nitrogen atmosphere. Initially sulfuryl chloride, S02C12,was used as the chlorinating agent. Nine equivalents of S02C12was added to a methylene chloride solution of ( ~ - B u ~ N ) ~atB-78 ~ H“C~ and the solution allowed to warm to room temperature. Low to moderate yields of BgC192-can be isolated from the nonvolatile residue (Scheme I). Subsequently it was discovered that N-chlorosuccinimide under similar conditions gives very good yields of the desired product. Use of N-bromosuccinimide produced the B9Br92salt in high yields. Periodination of B9H92-proceeded smoothly with excess elemental iodine in methylene chloride solution to give B&’-. Properties of B9Xg”. Salts of all three dianions are air-stable solids. The sodium salt of BgC19’- is stable to both 12 N HC1 (8) R. M . Kabbani and E. H. Wong, J . Chem. Soc., Chem. Commun., 462 (1978).
c3 HALOGEN
3
BORON
Figure 2.
and 6 N NaOH in aqueous solutions. The B9Brg2-and B9192salts are slightly less stable. This contrasts dramatically with the reported rapid acid hydrolysis of B9Hg2-,B9Br6H32-,and B9C18H2-s p e c i e ~ . ~Both ~ , ~the stability of the boron-halogen bonds and the enhanced steric bulk along with the higher symmetry of a perhalogenated polyhedron may contribute to the hydrolytic stability of these dianions. The infrared absorptions of all three show similar patterns in the boron-halogen and boron-cage vibration regions (850-1150 cm-’) as shown in Figure 1. The shift of these absorptions to lower frequencies upon changing the substituent from C1 to Br to I is similar to trends reported for the neutral B9X9(X = C1, Br)7dand the dianionic BloX12-(X = C1, Br, I) and Bl2XIz2-(X = C1, Br, I).5 This strongly suggests the adoption of similar polyhedral geometries for the B9X92species. In addition, the sensitivity of all these absorptions to the type of halogen also argues for the occurrence of considerable a-bonding interaction between the B9 cage and the terminal halogens. Their UV spectra also show a similar trend (Table I). The 28.9-MHz l l B N M R data are presented in Table 11. The two expected boron resonances (peak ratios 3:6) for a tricapped trigonal-prismatic D3hgeometry (Figure 2) are clearly observed for B9Br92-and B&-. These resonances are less well resolved in B9C1g2-, and the lower field signal appears as a shoulder to the higher field resonance. A similar trend of increasing separation between five- and six-coordinate boron shifts is seen in the BIOXlO2resonances6 B9X9 (X = CI, Br) and B9X9-. (X = C1, Br, I). It was originally observed that excess S02C12reacted with B9H9’to give only low yields of BgC19’- (5-15%). Removal of vol(9) F. Klanberg and E. L. Muetterties, Inorg. Chem., 5, 1955 (1966).
Inorganic Chemistry, Vol. 19, No. 2, 1980 453
Boron Halide Clusters and Radicals chart I
Scheme I1 BgHgZ-
___j
(BgrlxH,~xZ-)
I
__j
I
BgC18H2-
A9ClgZ-
I
I
BOROS HALIDE CLUSTER
NO. OF SKELETAL E L E C T R O N S ~ 20
-2e19
18
of formal skeletal e l e c t r o n s f o r
Figure 3. Room-temperature solution EPR spectra of the BgX9-w radicals. Table 111. Infrared Spectral Data for B,Cl,-., B,Br,’., in the 850-1100-cm-’ region
a
radical anion
frea ,a cm-
B,Cl,-. B,Br9-. B,19-.
1052 s, bd; 970 s, bd 1005 s, bd; 930 s, bd 963 s, bd; 285 s, bd
and BJ;.
Nujol mulls of the n-Bu,N salt.
atiles from the reaction mixture at room temperature gives a yellow oily residue which can be extracted by n-hexane to give an orange-yellow filtrate. A yellow-orange microcrystalline solid can be isolated from the hexane solution. UV, IR, and mass spectral data identified this as B9C19.7bYields of over 30% can be obtained, and this represents a uniquely convenient and selective synthesis of the neutral cluster without the usual need for electric-discharge apparatus and vacuumline separation^.'^,^^ The sulfuryl chloride appears to be both the chlorinating and the oxidizing agent. It seems reasonable that intermediate species of partially chlorinated B9 may be involved as in Scheme 11. It can be demonstrated that B9ClsH can indeed be readily chlorinated by S02C12to give B9C19. It has also been established that perhalogenated polyhedral boranes are more difficult to oxidize than the parent dianions.2b Direct oxidation of ( ~ - B U ~ N ) ~ with B ~thallic C ~ ~trifluoroacetate produced a dark brown product which was paramagnetic and was analyzed as (n-Bu4N)B9C19.Similar oxidations of B9Brg2-and B919” produced paramagnetic brown and violet species, respectively. It is also possible to use N-chlorosuccinimide (NCS) or N-bromosuccinimide (NBS) for these latter oxidations. An alternate synthesis for BgClg-. is via the one-electron reduction of BgC19 with a stoichiometric amount of n-Bu4NI. Similarly, B9Br9-. can be prepared from B9Br9. These species represent the first stable polyhedral borane radicals isolated. Previous reports of neutral boron radicals like BI2Clllhave been put in doubt by recent ~ ~ r k . As expected, further oxidation of the BgC19-q and B9Br9-. radicals with excess thallic trifluoroacetate produced the neutral B9C19and B9Br9clusters, respectively. We have not yet successfully isolated pure samples of the unknown B919 cluster by this method. A red-purple product of the oxidation of B919-. has proved to be relatively unstable. The decreased ability of iodine to back-bond and stabilize the B9 cage may well render it less accessible. (10) E. P. Schram and G. Urry, Inorg. Chem., 2, 405 (1963).
B
nine-boron polyhedra.
See r e f . 3b
Properties of B9X9--. Solution ESR spectra of these paramagnetic monoanions exhibited broad single resonances without fine structure (Figure 3). The signals shift to lower field and broaden increasingly upon going from B9C19-- to B9Br9-.to B919-.. Measured gvalues for the radicals are 2.018, 2.080, and 2.191, respectively. Their electronic spectra are presented in Table I. The IR absorptions in the cage and B-X region again show similarities with expected shifts to lower frequencies from C1 to Br to I substitution (Table 111). While it has not been possible to rigorously establish the geometries of these radical monoanions, all known nine-boron polyhedra possess the tricapped trigonal-prism (D3h)geometry. These include B9Hg2-,11BgC1g2-, B9Br92-,and B91g2-(vide supra). Additionally, neutral B9C19 and B9Br9clusters have been shown by X-ray diffraction to have essentially D3hgeometries.” It seems quite unlikely that these B9X9-. species, which represent the intermediate oxidation state of the redox series B9Xg2-,B9X9-., and B9X9,will adopt a geometry significantly different from the favored tricapped trigonal prism. Chemical Properties of BgX9--. All three monoanions exhibit good air stability both as solids and in aprotic solvents. Methylene chloride solutions of B9C19-. and B9Br9-. slowly decompose in air to give colorless solutions over a period of days. Under dry nitrogen atmosphere, all B9X9-. solutions are stable indefinitely at room temperature. Facile reductions to the parent dianions can be achieved with stoichiometric amounts of iodide. As described above, B9C19-. and B9Br9-. can be further oxidized to the neutral clusters. Their relative oxidizing strengths vary in the order BgC19-* < B9Br9-. < Bg19-.. This may again be an indication of the optimal ability of the chlorine substituents to back-donate into the electron-deficient B9 cage and stabilize the radical anion. The existence and isolation of these radicals and the known neutral B9X9species thus further support the multiple-bonding character of boron halide clusters. Limited structural data of the neutral boron chloride clusters indicate B-C1 distances ranging from 1.70 to 1.75 A (for example: B4C14, 1.70-1.71 A;13BsC18, 1.65-1.75 A;I4B9C19,1.72-1.75 A1*). Comparing these to the B-Cl range of 1.77-1.88 A in the (2n + 2)-electron borane derivatives such as 5,12-C12-m-C BloHlo(1.80-1.81 A),159,lO-C1 -1,7-CHPBloHs(1.77-1.80 &,16 m-B,oClloC2H2 (1.79-1.84 C2B4H5C1(1.82 A),18 and the polyhedral borane BloH7C132-(1.83-1.88 we can conclude that significant multibonding must exist in the boron halide clusters for their electron deficiency. ~ ~to ,compensate ~ ~
A),17
(11) L. J. Guggenberger, Inorg. Chem., 7 , 2260 (1968). (12) M. B. Hursthouse, J. Kane, and A. G. Masses, Nature (London), 228, 659 (1970). Note that the structural drawing is in error. Three bonds (13) (14) (15) (16) (17)
completing the tricapped trigonal prism are missing. M. Atoji and W. N. Lipscomb, Acta. Crystallogr., 6, 547 (1953). R. A. Jacobsonand W. N. Lipscomb, J . Chem. Phys., 31,605 (1959). H. V. Hart and W. N. Lipscomb, Inorg. Chem., 12, 2644 (1973). E. H. Wong and W. N. Lipscomb, Inorg. Chem., 14, 1350 (1975). J. A. Potenza and W. N. Lipscomb, Proc. Nafl.Acad. Sci. U.S.A.,56,
1917 (1966). (18) G. L. McKown and R. A. Beaudet, Inorg. Chem., 10, 1350 (1971). (19) F. E. Scarborough and W. N. Lipscomb, Inorg. Chem., 11, 369 (1972).
Wong a n d Kabbani
454 Inorganic Chemistry, Vol. 19, No. 2, 1980
was obtained. Anal. Calcd for C3zH,2N2B919:C, 22.29; H , 4.18; I, 66.23. Found: C, 22.38; H, 4.42; I, 66.58. Preparation of BgC19. From B9H9*-. A solution of ( ~ - B U ~ N ) ~ B ~ H ~ (200 mg, 0.34 mmol) in 10 mL of CH2C12was cooled to -78 OC. Twenty equivalents of SOzC12(550 kL, 6.8 mmol) was added via a syringe. The mixture was allowed to warm to room temperature and stirred for 2 h. The solvent and volatiles were removed with a mechanical-pump vacuum, and the orange oily residue was extracted with 10 mL of dry n-hexane. Filtration and removal of solvent yielded yellow-orange microcrystalline B9CI9 (49 mg, 0.1 2 mmol, 33%) identified by its IR, UV, and mass spectra. This can be further purified by sublimation in a vacuum line. From B9C1;. A mixture of 50 mg (0.076 mmol) of (n-Bu4N)B9CI9 and 100 mg (0.185 mmol) of T1(CF3C00)3was stirred in 5 mL of CH2CI2. After 0.5 h, the solvent was evaporated off and the residue extracted with 10 mL of hexane. From the extract was isolated 14 mg (0.033 mmol, 44%) of BgC19. Preparation of (n-Bu4N)B9CI9. From B9CI9,-. A solution of (nB U ~ N ) ~ B(200 ~ C Img, ~ 0.22 mmol) in 10 mL of CH2C12was added to T1(CF3C00)3(1 10 mg, 0.2 mmol) in a Schlenk tube. After stirring boranes. for 2 h, the solution was filtered through Celite and evaporated to Experimental Section dryness. The dark brown residue was washed with ethanol and ether to give 100 mg (0.15 mmol, 75%) of (n-Bu4N)B9CI9as brown flakes. All reactions were run under an atmosphere of dry nitrogen in From B9CI9. A 10-mL CH2C12solution of B9CI9(120 mg, 0.29 Schlenk glassware. Methylene chloride was distilled under nitrogen mmol) was added to (n-Bu,N)I (100 mg, 0.27 mmol), and the resulting from phosphorus pentoxide. T1(CF3C00)3,(n-Bu4N)C1,(n-Bu4N)I, solution was evacuated to dryness. The residue was washed with ether and SO2CI2were obtained from Aldrich Chemical Co. n-Hexane was to give 155 mg (0.23 mmol, 80%) of (n-Bu4N)B9C19as a brown dried by distillation from CaH,. ( ~ - B U ~ N ) was ~ B obtained ~ H ~ by microcrystalline solid. Anal. Calcd for C16H36NB9C1g: C, 29.1 7; literature methods.20 ( ~ - B u ~ N ) ~ B ~and C ~B9ClgH * H were prepared H , 5.46; CI, 48.43. Found: C, 29.39; H , 5.75; C1, 47.73. by Muetterties' p r o c e d ~ r e . ' ~ Preparation of ( n-Bu4N)B9Br9.A solution of (n-Bu4N),B9H9(500 I R spectra were recorded as Nujol mulls or CH2Clzsolutions on mg, 0.85 mmol) in 25 mL of CH2C12was cooled to -78 "C and 20 a Perkin-Elmer 337 spectrometer. The 28.9-MHz "B spectra were equiv (3.0 g, 16.9 mmol) of A7-bromosuccinimide added. After recorded on a Bruker W H 90-DX spectrometer with Fourier transform warming of the mixture to room temperature and 1 h of additional and deuterium lock. IlB shifts were referenced to external BF3.Et20. stirring, ether was added to precipitate the brown product. This was Visible and ultraviolet spectra were taken with a Cary 14 spectrofiltered and washed with ethanol to give 0.80 g of (n-Bu4N)B9Br9(0.75 photometer by using spectrograde CH,CN solvent. EPR data were mmol, 90%) as a dark brown solid. Anal. Calcd for C&36NB$r9: obtained on a Varian E-4 spectrometer using DPPH as frequency C, 18.15; H , 3.40; Br, 67.91. Found: C, 18.19; H , 3.51; Br, 65.95. marker. Preparation of B9Br9. A solution of 200 mg (0.19 mmol) of (nChemical analyses were performed by Schwarzkopf Microanalytical Bu4N)B9Br9in 10 mL of CH2C12was added to 0.3 g (5.5 mmol) of Laboratory, Woodside, N.Y. T1(CF3C00)3and the resulting suspension stirred for 2 h. The dark Preparation of ( ~ - B u ~ N ) ~ B , CFrom I , . S02C12. An amount of 200 orange-red solution was evaporated to dryness and the residue extracted mg (0.34 mmol) of ( ~ - B U ~ N ) was ~ B dissolved ~ H ~ in 5 mL of CH2CI2 with 10 mL of n-hexane. Filtration and removal of solvent yielded in a Schlenk tube and chilled in a dry ice-acetone bath. A 2 7 5 - ~ L 73 mg (0.09 mmol, 48%) of an orange-red solid identified as B9Br9 (3.4-mmol) sample of SO2CI2was slowly added via a syringe. A brown by its IR, UV, and mass spectra. It can be further purified by coloration developed instantaneously. After warming to room temsublimation. perature over a period of 1 h, the solution was evacuated to dryness Preparation of (n-Bu4N)B919. With NBS. A solution of 200 mg with a mechanical pump. The brown oily residue was extracted with (0,116 mmol) of (n-Bu4N),B919in 10 mL of CH2CI2was added to 5 mL of CH2CI2 and filtered through Celite. Addition of ether 41 mg (0.23 mmol) of N-bromosuccinimide and the mixture stirred precipitated 180 mg (0.20 mmol, 59%) of ( ~ - B U ~ N ) ~ B as&a Iwhite ~ overnight at room temperature. Addition of ether precipitated a violet powder. Recrystallization from CH2C12-ether gave microcrystalline solid of crude (n-Bu4N)B919. This was washed with ethanol and ether product of good purity. From N-Chlorosuccinimide. A solution of ( ~ - B u ~ N ) ~(1B.O~g,H ~ to give 140 mg (0.094 mmol, 81%) of the product. With T1(CF3C00)3. A solution of 250 mg (0.13 mmol) of (n1.7 mmol) in 25 mL of CH2C12was cooled to -78 OC. N-ChloroB u ~ N ) ~ in B 6~ mL I ~ of acetone was added to 70 mg (0.13 mmol) of succinimide (2.1 g, 15.7 mmol) was added and the reaction mixture T1(CF3C00)3. After 0.5 h, the solvent was removed, and the violet allowed to warm to room temperature and stirred for 1 h. Addition residue was washed with ethanol to yield 160 mg (0.1 1 mmol, 82%) of ethyl ether precipitated the product. This was washed with ethanol C, 12.96; H , 2.43; of (n-Bu4N)B919. Anal. Calcd for C16H36NB9Br9: followed by ether to give ( ~ - B U ~ N ) ~ B (1.35 ~ C g. & 1.5 mmol, 88%). I, 77.07. Found: C, 13.27; H, 2.56; I, 76.29. Anal. Calcd for C32H72N2B9C19: C, 42.64; H , 7.99; C1, 35.46. Found: Reduction of ( n-Bu4N)B9X9.Stoichiometric amounts of the (nC, 42.91; H, 8.06; C1, 34.94. Bu4N)B9X9salt and (n-Bu4N)I were dissolved in CH2C12. After 5 Preparation of ( ~ - B I L , N ) ~ B ~ A B ~solution ~. of (n-Bu4N),B9H9(0.50 min, the solvent was removed and the residue washed with CHC1,. g, 0.85 mmol) in 25 mL of CH2C12was cooled to -78 OC. NThe crude (n-Bu4N),B9X9 was recrystallized from CH2C12-ether. Bromosuccinimide (1.36 g, 7.62 mmol) was added and the suspension Yields of over 90% were obtained. warmed to room temperature. After 1 h of additional stirring, diethyl Interconversion of B9C18H2-and B9ClgH. From BgClgH to B9C18H2-. ether was added to precipitate the product. After ethanol and ether A solution of B9C18H (38 mg, 0.1 mmol) in 10 mL of CH2CI2was washing, the yield of ( ~ - B U ~ N ) was ~ B 1.10 ~ B g~ (0.84 ~ mmol, 98%). added to (n-Bu,N)I (100 mg, 0.27 mmol), and the resulting yellowRecrystallization from acetone-n-hexane gave crystals. Anal. Calcd orange solution was evaporated to dryness and the residue washed for C32H72N2B9Br9: C, 29.53; H, 5.53; Br, 55.26. Found: C, 29.86; with ether to give 56 mg (0.09 mmol, 90%) of ( ~ - B U ~ N ) ~ B ~asC I ~ , H H , 5.74; Br, 54.88. Preparation of ( ~ - B U ~ N ) ~ B A ~solution I+ of ( ~ - B U ~ N ) (300 ~ B ~ H ~ a white solid. From B9Cl8HZ-to B9C18H. A solution of (n-Bu4N)2B9C18H(1 50 mg, 0.51 mmol) in 25 mL of CH2CI2was cooled to -78 "C. Nine mg, 0.17 mmol) in 10 mL of CH2Clzwas added to 50 mg (0.09 mmol) equivalents of iodine (1.20 g, 4.7 mmol) was added and the mixture of TI(CF3C00),. After stirring for 2 h, the red-brown solution was allowed to warm to room temperature. The brown suspension was filtered through Celite and evaporated to dryness. The red-brown stirred for 1 h and ether added to complete precipitation of the product. residue was washed with ethanol and ether to give 85 mg (0.13 mmol, After CHCI3 washing, 0.70 g of ( ~ - B u ~ N ) ~ (0.41 B & mmol, 80%) 74%) of (n-Bu4N)B9C18H.This was redissolved in 10 mL of CH2C12 and added to 100 mg (0.18 mmol) of T1(CF3C00),. After 0.5 h, the solvent was removed and the brown residue extracted with n(20) J. C. Carter and P. H. Wilks, Inorg. Chem., 9, 1777 (1970).
Conclusions We have prepared the perhalogenated B9X9*-derivatives and novel B9X9-. radicals and established t h e interconversions between BgXg2-, B9X9-., and B9X9. This represents the first successful demonstration of the redox relationship between formally (2n 2 ) , ( 2 n 1). and 2n polyhedral boranes. We have also confirmed t h e relationship between the previously reported B9C18H2-and B9C18H species. A summary of these redox conversions is presented in C h a r t I. If confirmed, the postulated retention of t h e parent D3h geometry for all t h r e e cluster classes would constitute a rare e x a m p l e of a nonmetallic cluster a b l e t o maintain its basic s t r u c t u r e over at least three oxidation states. F u r t h e r m o r e , the observed stability of all the perhalogenated boranes studied here convincingly attests to t h e effectiveness of halogen substituents in back-bonding to a n d in stabilizing of polyhedral
+
+
455
Inorg. Chem. 1980, 19, 455-451 hexane. Filtration and evaporation of solvent yielded a yellow-orange solid identified as B9C18H(15 mg, 0.04 mmol, 34%).
Acknowledgment* We are grateful to the donors Of the Petroleum Research Fund, administered by the American Chemical Society, for financial support. We also thank Dr. N. D. Chasteen for aid with the EPR work and Dr. E. I. Tolpin, Department of Chemistry, University of Louisville,
for obtaining the 'lB N M R spectra. Registry No. (n-Bu4N),B9C19, 68694-93-9; ( ~ - B U ~ N ) ~ B ~ B ~ ~ , 72402-96-1; (~-Bu~N)~B&,,72402-94-9; B9C19, 3 1304-34-4; (nBU4N)B9C19,72402-98-3; (n-Bu4N)B9Br9, 72402-95-0; B9Br9, 12589-31-0; ( n - ~ u 4 ~ ) ~72403-00-0; 9~9, B~CI~H 72275-1 , 1-7; (nB u ~ N ) ~ B ~ C ~72402-97-2; ,H, (n-Bu4N)B9C18H,72402-99-4; (nB u ~ N ) ~ B 68380-71-2. ~H~,
Contribution from the Department of Chemistry, Purdue University, West Lafayette, Indiana 47907
Molecular Addition Compounds. 7. Synthesis of Addition Compounds of Boron and Trifluoride, Borane, and Alane with N,N,N/,N'-Tetramethylethylenediamine Triethylenediamine by Precipitation from Ether Solvents' HERBERT C. BROWN* and BAKTHAN SINGARAM2 Received August 14, 1979 Triethylenediamine (TED) precipitates BF3 from diethyl ether (Et20) as TEDQBF3 and as TEDsBF, from tetrahydrofuran (THF). N,N,N',N'-Tetramethylethylenediamine(TMED) and TED precipitate BH3 from both Et20 and THF as TMED.2BH3 and TED.2BH3, respectively. From EtzO, TMED precipitates AlH3 as TMED.2AlH3. In THF, TMED reacts with A1H3 to afford TMED.A1H3. Thus the patterns of behavior exhibited by BF3, BH3, and AIHl with TED and TMED in EtzO and in T H F are all different. Since TMED-A1H3is modestly soluble in THF, TMED cannot precipitate alane quantitatively from this solvent. However, TED reacts instantly and quantitatively with alane in E t 2 0 and T H F to give the highly insoluble mono adduct TED.A1H3. Consequently, the quantitative precipitation of alane from ether solvents is feasible with TED.
Introduction Over the years, various workers have carried out experiments involving addition compounds of N,N,N',N'-tetramethylethylenediamine (TMED) and triethylenediamine (TED) with boron trifluoride, borane, and alane.3-8 These adducts are highly insoluble in the usual organic solvents (THF, EtzO, CHC13,pentane, and benzene). During the course of our work, it became desirable to achieve the convenient precipitation of borane and alane from ether solvents. Surprisingly, no work has been reported in the literature on the precipitation of borane and alane from their solution in ether solvents using TMED or TED. Recently we reported the successful precipitation of BF3 from such ether solvents by TMED and ethylenediamine (EDA).'q3 Irrespective of the mode of addition or the amount of the reactants, TMED always precipitates BF3 as TMED.2BF3.3 The reaction between EDA and BF3 affords either the mono or the bis adduct, depending upon the solvents utilized.' In continuation of the above study, we now wish to report our exploration of the precipitation under standardized conditions of boron trifluoride, borane, and alane from ether solvents (EtzO, THF) with TMED and TED. Experimental Section The reaction flasks and other glass equipment used for experiments were oven-dried and assembled in a stream of dry nitrogen gas. The special techniques for the manipulation of air-sensitive materials are described e l ~ e w h e r e . ~Et20.BF3 and TMED were distilled from calcium hydride. TED was purified by sublimation under reduced pressure. Aluminum hydride was prepared according to the published (1) Part 6: Brown, H. C.; Singaram, B. Inorg. Chem. 1979, 18, 5 3 . (2) Postdoctoral research associate on Grant No. GM 10937 from the
National Institutes of Health.
(3) Brown, H. C.; Singaram, B.; Schwier, J. R. Inorg. Chem. 1979, 18, 51. (4) McDivitt, J. R.; Humphrey, G. L. Spectrochim. Acta, Part A 1974,3Oa,
1021. (5) Miller, N. E.; Muetterties, E. L. J . Am. Chem. SOC.1964, 86, 1033. (6) Gatti, A. R.; Wartik, T. Inorg. Chem. 1966, 5 , 2075. (7) Davidson, J. M.; Wartik, T. J . Am. Chem. SOC.1960, 82, 5506. (8) Dilts, J. A,; Ashby, E. C. Inorg. Chem. 1970, 4 , 8 5 5 . (9) Brown, H. C.; Kramer, G. W.; Levy, A. B.; Midland, M. M. "Organic
Syntheses via Boranes"; Wiley-Interscience: New York, 1975; Chapter 9.
0020-1669/80/1319-0455$01 .OO/O
procedure.1° The 'H NMR, IIB NMR, and 21A1 N M R spectra were recorded on Varian T-60 and FT-80A instruments. The 'H, I'B, and 27Alchemical shifts are in 6 relative to Me4Si,Et20-BF3,and Al(N03)3 standards, respectively. Infrared spectra were recorded with the Perkin-Elmer 700 spectrometer. Precipitation of Boron Trifluoride with Triethylenediamine, (a) Determination of Stoichiometry by 'HNMR. Two different reactions were carried out in individual centrifuge vials maintained at 25 "C. The vials were charged with TED (5 mmol), benzene (3.0 mmol, internal standard), and CC14 ( 5 mL). An aliquot (0.6 mL) was taken from the first vial, and the amount of TED was estimated via 'H NMR. To the second vial was added 5.0 mmol of Etz0.BF3 with stirring. The IH N M R spectrum of the supernatant liquid, following centrifugation, indicated that all TED had been precipitated from solution, and no signal attributable to TED was detectable. (b) Determination of Stoichiometry by GLC. In a 50-mL centrifuge vial were dissolved 5.0 mmol of TED and 3.0 mmol of n-dodecane (internal standard) in 10 mL of THF. The amount of TED present in the solution was determined by GLC analysis with a 6 ft X 0.25 in. column packed with 10% SE-30 on Chromosorb W. The solution was then treated with 5.0 mmol of Et20.BF3 with constant stirring; a white solid precipitated. GLC analysis of the supernatant liquid indicated that it was free of TED. The adduct was collected by centrifugation, washed sevtral times with n-pentane, and dried. There was obtained 0.88 g (98% yield) of TED.BF3: mp 199-201 OC;ll IR and IH N M R spectra superimposable with those reported in literature;" llB N M R (CH3CN) 6 -0.32 (q, J = 13 Hz). When the same reaction was carried out in diethyl ether, a different result was realized. Thus, treatment of 5.0 mmol of TED in E t 2 0 with 5.0 mmol of Et20.BF3 yielded a precipitate. GLC analysis of the supernatant liquid revealed the presence of 2.5 mmol of residual TED. The reaction mixture was treated further with 5.0 mmol of Et20.BF3. The GLC analysis now indicated no TED in the solution. The adduct was collected by centrifugation, washed several times with Et20,and dried. There was obtained 1.23 g (99% yield) of TED.2BF3: mp >300 "C; IR spectrum identical with that reported in the literature: 'H N M R (acetone-d6) 6 3.47 (s, 12 H); IlB N M R (CH3CN) 6 -0.24 (q, J = 12 Hz). Precipitation of Borane with N,N,N',N'-Tetramethylethylenediamine and Triethylenediamine. Determination of Stoichiometry. Identical reactions were carried out in THF and in E t 2 0 at 25 O C . The following (10) ( 1 1)
Brown, H. C.; Yoon, N. M. J . A m . Chem. SOC.1966,88, 1464. Van Paasschen, J. M.; Geanangel, R. A. Can. J . Chem. 1975,53,723.
0 1980 American Chemical Society
